A copper alloy bar and a preparation method thereof

Abstract

The present invention discloses a copper alloy bar, characterized in that: the mass percentage composition of the copper alloy is Si: 1.0 - 2.0 wt%, Mn: 0.3 - 0.8 wt%, Zn: 0.01 - 1.2 wt%, Fe ≤ 0.10 wt%, Pb ≤ 0.007 wt%, and the balance is Cu and inevitable impurities. By controlling the contents of Si, Mn, and Zn in the copper alloy and controlling the proportion of the MnSi brittle phase, excellent cold heading performance and mechanical properties of the material are obtained, with a tensile strength of 360 - 450 Mpa, a yield strength of 310 - 400 MPa, a reduction of area Z of 40 - 60%, and a hardness HV of 100 - 150.

Description

Technical Field

[0001] The invention belongs to the technical field of copper alloys, and in particular relates to a copper alloy bar and a preparation method thereof. Background Art

[0002] Fasteners are a general term for a type of mechanical parts used to fasten two or more parts into a whole. C65100 is made of Si and Mn as the main alloying elements, has good mechanical properties, and can be used for cold heading into bolts, screws, nuts and other fasteners. Cold heading is a processing method that utilizes the plastic deformation of metal under the action of external force, and with the help of a mold, redistributes and transfers the metal volume to form the required parts or blanks. The cold heading process is most suitable for the production of fasteners. The cold heading process replaces the cutting process, has high production efficiency, and saves raw materials.

[0003] Good cold heading performance means that the copper alloy has a low deformation resistance and can withstand a large degree of deformation without cracking. The section shrinkage rate and yield strength can reflect the quality of the material's cold heading performance. The greater the section shrinkage rate and the lower the yield strength, the better the material's cold heading performance. However, as a fastener, it needs to pass the torque test, so it needs to maintain a high strength to prevent the fastener from deforming when it is stressed.

[0004] Although C65100 has excellent cold deformation processing performance, when it is cold headed into fasteners such as screws and nuts, the deformation generally reaches 60-90%, which is easy to form tiny cracks invisible to the naked eye. During the service life of the material, under the action of external forces, the fine cracks expand and crack, posing a hidden danger to the safe operation of the equipment. The main reasons are: uneven grain size, the difference between the minimum and maximum grain sizes is about 70μm, the grain orientation is disordered and anisotropic, and the structural defects cause the deformation and stress state of each grain to be different when the material is cold headed. This difference can be reflected in different parts of the macro-scale sample, and also exists inside grains with different orientations. Even in different areas of the same grain, the difference in deformation and stress state will lead to extremely uneven stress distribution. The tensile stress is the largest at the part with the largest cold deformation, and it is most likely to produce small cracks. As a result, the C65100 silicon-manganese copper fasteners currently on the market cannot be used in scenarios with extremely high requirements for material safety performance. Therefore, it is necessary to improve the current silicon-manganese copper composition and processing technology to prepare silicon-manganese copper rods and wires with uniform grain size and consistent orientation to meet the needs of aerospace, navigation, electric power and other industries for silicon-manganese copper. Summary of the invention

[0005] The first technical problem to be solved by the present invention is to provide a copper alloy bar with excellent cold heading performance.

[0006] The second technical problem to be solved by the present invention is to provide a method for preparing copper alloy rods.

[0007] The technical solution adopted by the present invention to solve the first technical problem is: a copper alloy rod, characterized in that the mass percentage composition of the copper alloy is Si: 1.0-2.0wt%, Mn: 0.3-0.8wt%, Zn: 0.01-1.2wt%, Fe≤0.10wt%, Pb≤0.007wt%, and the balance is Cu and unavoidable impurities.

[0008] Si: The maximum solubility of Si can reach 5.3% at 852℃, but it decreases with decreasing temperature. Si can improve the hardness and strength of Cu. When the Si content is less than 1%, there will be a contradiction between alloy strength and forgeability. It is necessary to increase the processing rate of tensile deformation of rods and wires to meet the requirements of fasteners for the tensile strength of silicon manganese copper rods and wires ≥ 350MPa. The negative problem brought about is that the strong work hardening effect makes the forgeability of silicon manganese copper worse, and cracks are easily generated during cold heading deformation; however, with the increase of Si content, after the Si content exceeds 2%, the forgeability of silicon manganese copper begins to decrease, mainly because Si combines with Mn to form a large number of MnSi brittle phases. Therefore, the Si content of the silicon manganese copper of the present invention is controlled at 1.0-2.0wt%.

[0009] Mn: Mn is dissolved in copper, which can improve the softening temperature of silicon manganese copper on the one hand, and improve the mechanical properties and processing properties of silicon manganese copper on the other hand. When the Mn content is lower than 0.3%, adjusting the content of other alloy elements in silicon manganese copper and the processing technology cannot make the softening temperature of silicon manganese copper reach above 430℃; when Mn exceeds 0.8%, the incompletely dissolved Mn combines with Si to form a MnSi brittle phase, which reduces the forgeability of silicon manganese copper.

[0010] Zn: Zn is more active than Si and Mn. A small amount of Zn can prevent oxygen in the melt from combining with Si and Mn to produce SiO2 and MnO2 oxides, and prevent Si and Mn oxides from remaining in the melt. Zn can also narrow the liquid-solid range of silicon-manganese copper and avoid porosity in the ingot, so the lower limit of the effective content of Zn is not less than 0.01%, but the maximum content of Zn is not more than 1.2%, otherwise the corrosion resistance of the alloy will deteriorate.

[0011] Fe: At room temperature, Fe exists in Cu basically in the form of hard points, which will increase the hardness of silicon-manganese copper and reduce the forgeability of silicon-manganese copper. Therefore, the Fe content in the alloy of the present invention is controlled below 0.10%, which has little effect on the forgeability of silicon-manganese copper.

[0012] Pb: Pb is almost insoluble in silicon manganese copper. Pb is distributed in the grain boundaries in a free state, making the grain boundaries exhibit cold brittleness, which causes crack sources to easily occur at the grain boundaries during the cold heading deformation process of silicon bronze. In addition, when the Pb content in silicon manganese copper reaches more than 0.007%, during hot working, the Pb on the grain boundaries shows hot brittleness, resulting in hot working cracking. Therefore, the impurity Pb in the silicon manganese copper of the present invention needs to be strictly controlled below 0.007%.

[0013] Preferably, the microstructure of the copper alloy has the α phase as the matrix phase, and the area ratio of the MnSi phase is below 0.2%.

[0014] Preferably, the average grain size of the copper alloy is 30 - 50 μm, the proportion of grains with a grain size greater than 70 μm is ≤3%, and the proportion of grains with a grain size less than 10 μm is ≤5%. The average grain size of the copper alloy of the present invention is 30 - 50 μm because the internal structure control requirements of silicon manganese copper for cold heading are different from those of silicon manganese copper for other uses. If the grain size is too small, the number of grain boundaries hindering slip increases, the number of dislocation pile-ups at the grain boundaries during the deformation process also increases, the yield strength increases, the deformation resistance increases, and cold heading forming becomes difficult, and cracking is likely to occur. If the grain size is too large, the surface of the product after cold heading will be rough and obvious wrinkles will be generated. The proportion of grains with a grain size greater than 70 μm is ≤3%, and the proportion of grains with a grain size less than 10 μm is ≤5% because the deformation of the metal during cold heading occurs due to the slip of grains and the deformation of the grains themselves. The uniformity of the grain size is good, the deformation can be evenly dispersed to each grain, the stress concentration caused is small, and the chance of cracking is also reduced.

[0015] Preferably, the area ratio of twins in the structure of the copper alloy does not exceed 10% of the total grain area, and the area ratio of deformation twins does not exceed 20% of the total twin area. The area ratio of twins does not exceed 10% of the total grain area because after the appearance of twins, the twin boundaries will play a hardening role and reduce the plasticity of the alloy. The area ratio of deformation twins does not exceed 20% of the total twin area because annealing twins are isotropic, while deformation twins will have different preferred orientations due to different applied stresses, so they are anisotropic, resulting in annealing twins being less likely to generate cracks than deformation twins during the cold heading deformation process.

[0016] The technical solution adopted by the present invention to solve the second technical problem is: a preparation method of a copper alloy bar, characterized in that the technological process of the copper alloy includes: melting → casting → extrusion → wire drawing → annealing, pickling → finished product drawing → low-temperature annealing; the low-temperature annealing process is protected by a reducing atmosphere, the annealing temperature is 200 - 350 °C, the holding time is 2 - 6 h, and it is cooled to below 60 °C before discharging.

[0017] Preferably, the feeding order for smelting is electrolytic copper → copper-silicon master alloy → copper-manganese master alloy → zinc. In the alloy, Si can reduce the solubility of H (hydrogen) in the melt, while Mn can increase the solubility of H in the melt. Zn is the most active and easily combines with oxygen. Therefore, adding Zn at the end can reduce the oxides of Si and Mn in the melt and improve the metallurgical quality of the melt.

[0018] Preferably, the casting temperature for casting is 1220 - 1270 °C, the drawing speed is 30 - 70 mm / min, the primary cooling water flow rate is 10 - 20 m 3 / h, and the secondary cooling water flow rate is 0.1 - 3 m 3 / h, and the cooling water pressure is 0.01 - 0.06 MPa. Since Si severely reduces the thermal conductivity of copper, the solidification rate of the alloy during casting is slow. For alloys with poor thermal conductivity, to ensure that the alloy has sufficient solidification time and avoid stress cracks that are likely to occur when the cooling intensity is high, i.e., when the outer layer of the ingot solidifies while the core is still in a molten state, the silicon-manganese copper casting of the present invention requires weak secondary cooling and low-speed drawing. If the drawing speed is too slow, or the primary and secondary cooling water flow rates are too large, the liquid-solid interface moves up into the mold, the contact area between the solidified shell and the inner wall of the mold increases, the frictional resistance increases, and the surface quality of the ingot is poor. If the drawing speed is too fast, and the primary and secondary cooling water flow rates are too small, the liquid-solid interface moves down, the distance below the mold outlet becomes longer, the liquid cavity becomes deeper, and the thin solidified shell layer will be melted and broken by the high-temperature liquid copper in the core, resulting in copper leakage.

[0019] Preferably, the heating temperature of the ingot for extrusion is 820 - 900 °C, the extrusion speed is 9 - 14 mm / s, and the extrusion ratio is 80 - 200. If the extrusion ratio is lower than 80, due to the low degree of extrusion deformation, the driving force for dynamic recrystallization is small, and the grains of the extrusion billet are coarse. However, if the extrusion ratio is too high, exceeding 200, the severe extrusion deformation causes a high lattice distortion energy and a large driving force for dynamic recrystallization, resulting in fine recrystallized grains smaller than 20 μm. The increase in grain boundaries, where the atomic arrangement is very irregular and has high energy, makes it difficult to adjust the finished product grain size to 30 - 50 μm through the process. When the extrusion speed is low, it takes a longer time to extrude the entire ingot, the temperature drop of the ingot is fast, the deformation resistance at the end of the ingot increases, and the extrusion of the entire ingot cannot be completed smoothly. When the extrusion speed is too fast, the extrusion force increases sharply, exceeding the limit pressure of the extruder, causing the extrusion rod to break. The alloy of the present invention is suitable for extrusion at a speed of 9 - 14 mm / s.

[0020] Preferably, the processing rate of the wire drawing should be controlled at 20-60%, and the processing rate of the finished product stretching should be controlled at 3-17%. If the wire drawing processing rate is lower than 20%, the degree of cold deformation is low, the lattice distortion caused is small, the degree of atomic dislocation is low, and deformation twins are likely to occur. After annealing, some deformation twins disappear and new annealing twins are formed; as the degree of cold deformation increases, when the wire drawing processing rate exceeds 60%, the structure of each part of the billet is deformed sufficiently, the original grains of the extruded billet are completely broken, the number of recrystallization nuclei increases significantly, the recrystallized grains are fine, the deformation resistance increases, and cold heading forming becomes difficult, and cracking is likely to occur. Based on the control of the mechanical properties of the finished product, if the processing rate of the finished product is lower than 3%, since the deformation amount of the wire billet drawn through the die is too small, the deformation only occurs on the surface layer of the wire billet, resulting in the surface metal flow rate being greater than that of the central layer metal, and striae will appear on the surface of the finished product; after the processing rate exceeds 17%, the plasticity of the alloy becomes poor due to work hardening, and cold heading is prone to cracking.

[0021] Preferably, the annealing temperature is 520-600°C. Starting from room temperature, after heating to the set temperature, the holding time is 120-300 min. The higher the annealing temperature, the stronger the atomic diffusion ability, the easier the grain boundary migration, and the faster the grain growth. In the present invention, when the annealing temperature of the silicon-manganese-copper alloy is lower than 520°C, on the one hand, it is difficult for the deformation twins generated by tensile deformation to disappear; on the other hand, the recrystallized grain size will be small, the average grain size is less than 30 μm, the cold heading deformation resistance is large, and cracks are likely to appear; after the annealing temperature exceeds 600°C, the grains begin to become coarse, the average grain size exceeds 50 μm, wrinkles are easily formed on the surface of the product after cold heading, and it is easy to cause copper adhesion on the stamping die, resulting in a decrease in die life. If the holding time is short, less than 120 min, the recrystallization is insufficient, especially in the case of a large loading amount in the furnace, it is more prominent; if the holding time is long, exceeding 300 min, it is extremely easy to cause coarse grains. After annealing, the surface oxide scale of the wire billet is removed by pickling.

[0022] Compared with the prior art, the advantages of the present invention are as follows: By controlling the contents of Si, Mn, and Zn in the copper alloy and the proportion of the brittle phase of MnSi, excellent cold heading performance and mechanical properties of the material are obtained, with a tensile strength of 360-450 Mpa, a yield strength of 310-400 MPa, a reduction of area Z of 40-60%, and a hardness HV of 100-150. Specific embodiments

[0023] The present invention will be further described in detail below with reference to the embodiments.

[0024] The present invention provides 6 examples and 2 comparative examples, and the specific compositions are shown in Table 1.

[0025] The preparation steps of the examples are as follows:

[0026] 1) Melting: Charge materials according to the required composition. The charging sequence is: electrolytic copper → copper-silicon master alloy → copper-manganese master alloy → zinc. The melting temperature is 1200 - 1280 °C.

[0027] 2) Casting: Casting temperature: 1220 - 1270 °C, drawing speed: 30 - 70 mm / min, primary cooling water flow rate: 10 - 20 m 3 / h, secondary cooling water flow rate: 0.1 - 3 m 3 / h, cooling water pressure: 0.01 - 0.06 MPa, ingot sawing specification: φ180 - 260 mm * 500 - 800 mm.

[0028] 3) Extrusion: Ingot heating temperature: 820 - 900 °C, extrusion speed: 9 - 14 mm / s, extrusion ratio: 80 - 200. After the extruded billet is extruded from the die, it is coiled and wound up.

[0029] 4) Coiling and drawing: The processing rate of coiling and drawing is 20 - 60%;

[0030] 5) Annealing and pickling: Annealing temperature: 520 - 600 °C. Start heating from room temperature. After reaching the set temperature, the holding time is: 120 - 300 min.

[0031] 6) Finished product drawing: The bars are drawn, straightened, polished, and sawed into straight bars through combined drawing. The wires are drawn into coiled wires through an inverted wire drawing machine. The processing rate is: 3 - 17%.

[0032] 7) Low-temperature annealing: Protected by a reducing atmosphere of H2, annealing temperature: 200 - 350 °C, holding time: 2 - 6 h, cooled to below 60 °C and then taken out of the furnace.

[0033] 8) Final inspection. The control of key process parameters is shown in Tables 2 and 3.

[0034] Comparative example 1 is commercially available C65100 φ10.5 wire.

[0035] Comparative example 2 is commercially available C65100 φ17.5 bar.

[0036] The following tests are carried out on the microstructures of the obtained examples and comparative examples, and the results are recorded in Table 4.

[0037] Grain size, proportion of different grains, and distribution quantity of brittle phases are observed under a scanning electron microscope;

[0038] The following performance tests are carried out on 6 examples and 2 comparative examples, and the results are recorded in Table 5.

[0039] Tensile strength, yield strength Rp 0.2Elongation at break and reduction of area: Tested in accordance with GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature".

[0040] Hardness HV: Tested in accordance with GB / T 4340.1-2009 "Metallic materials - Vickers hardness test - Part 1: Test method".

[0041] Upset test: The specimen is made into a cylinder with a height 1.5 times the original diameter of the specimen, and then flattened on a hydraulic press until the first visible crack appears on the specimen surface. The degree of compression (H0: The original height of the cylindrical specimen, H k : The height of the specimen when the first visible crack appears on the side surface during the flattening of the specimen), the value is recorded in Table 5. The larger the ε c value, the better the forgeability of the specimen.

[0042] Torque test: The breaking torque of bolts or screws is determined in accordance with the method in GB / T 3098.13-1996 "Mechanical properties of fasteners - Torque test and breaking torque of bolts and screws - Nominal diameters 1 to 10 mm", and recorded in Table 5.

Claims

1. A copper alloy bar, characterized in that: The mass percentage composition of the copper alloy is: Si: 1.0 - 2.0 wt%, Mn: 0.3 - 0.8 wt%, Zn: 0.01 - 1.2 wt%, Fe ≤ 0.10 wt%, Pb ≤ 0.007 wt%, and the balance is Cu and inevitable impurities; The microstructure of the copper alloy has α-phase as the matrix phase, and the area proportion of MnSi phase is below 0.2%; The average grain size of the copper alloy is 30 - 50 μm, the proportion of grains with grain size greater than 70 μm is ≤ 3%, and the proportion of grains with grain size less than 10 μm is ≤ 5%; The area proportion of twins in the microstructure of the copper alloy does not exceed 10% of the total grain area, and the area proportion of deformation twins does not exceed 20% of the total twin area.

2. A preparation method of the copper alloy bar according to claim 1, characterized in that, The technological process of the copper alloy includes: melting → casting → extrusion → coil drawing → annealing, pickling → finish drawing → low-temperature annealing; the low-temperature annealing process is protected by a reducing atmosphere, annealing temperature: 200 - 350 °C, holding time: 2 - 6 h, and cooling to below 60 °C before discharging.

3. According to the preparation method of the copper alloy bar according to claim 2, characterized in that: The charging sequence of the melting is electrolytic copper → copper-silicon master alloy → copper-manganese master alloy → zinc.

4. According to the preparation method of the copper alloy bar according to claim 2, characterized in that, The casting temperature of the casting: 1220 - 1270 °C, the drawing speed: 30 - 70 mm / min, the primary cooling water flow rate: 10 - 20 m 3 / h, the secondary cooling water flow rate: 0.1 - 3 m 3 / h, the cooling water pressure: 0.01 - 0.06 MPa.

5. According to the preparation method of the copper alloy bar according to claim 2, characterized in that: The heating temperature of the ingot for extrusion is: 820 - 900 °C, extrusion speed: 9 - 14 mm / s, extrusion ratio: 80 - 200.

6. According to the preparation method of the copper alloy bar according to claim 2, characterized in that: The processing rate of the coil drawing needs to be controlled at 20 - 60%, and the processing rate of the finish drawing needs to be controlled at 3 - 17%.

7. According to the preparation method of the copper alloy bar according to claim 2, characterized in that: The temperature of the annealing is 520 - 600 °C, heating starts from room temperature, and after reaching the set temperature, the holding time is: 120 - 300 min.